This book provides an efficient introduction to fundamental and advanced digital transmission technologies in current and future wireless communication systems. The objective is to help students and engineers quickly grasp the operating principles and design trade-offs of various wireless transmission technologies, which will enable them to carry out product development or perform academic research in the field. With sufficient theoretical depth, the book covers large-scale channel effects; multipath fading; digital transmission over flat fading; fading mitigation through diversity combining; transmission over frequency selective fading; spread spectrum transmission; channel capacity and coding; channel adaptive transmission; MIMO transmission; and advanced topics including multiuser diversity transmission, cooperative relay transmission and multiuser MIMO transmission. The material is presented without assuming an extensive digital communications background from the readers. The design principles of these technologies are manifested with over 100 carefully designed illustration and over 60 problem-solving examples. The readers can also check their own understanding with extra practice problems at the end of each chapter. Special emphasis is placed on the important trade-off analysis of performance versus complexity.

Wireless communications is a fascinating field with extensive scope. This book primarily focuses on the point-to-point wireless transmission technologies. In this introductory chapter, we first present a brief overview of wireless communications. Then the access of wireless communication medium, the radio spectrum, is discussed, where sample schemes for both multiple access and random access are introduced. After that, we discuss the available duplexing schemes for two-way wireless communication systems. With the point-to-point transmission scenario thus established, the chapter is concluded with an outline of digital wireless transmission technologies.

The most distinguishing characteristic of wireless communication systems is the wireless channel, which has important implications on the design and analysis of wireless transmission technologies. In this chapter, we first provide an overview of wireless channel modeling. Then, the popular models for large-scale channel effects, i.e., path loss and shadowing, are presented. After that, path loss models and shadowing model are respectively applied to the cochannel interference analysis and outage/coverage analysis of wireless communication systems. The fundamental design principle of cellular system is also presented. The small-scale channel effects will be considered in the next chapter.

Fading characterizes the effect of random superposition of signal copies received from different propagation paths. These signal replicas may add together constructively or destructively, which leads to a large variation in received signal strength. Multipath fading manifests itself in a much smaller spatial scale than path loss and shadowing, and therefore, is called the small-scale effect of wireless channel. In this chapter, we first develop the general model for multipath fading channels. Then, we discuss the classification of fading channels based on their time domain and frequency domain characteristics. Finally, we present simplified models for two important types of multipath fading channels, which are widely used in the design and analysis of digital wireless transmission systems.

This chapter studies the effect of fading channels on digital wireless transmission. After reviewing the basics of digital bandpass modulation, we investigate the effect of channel phase and channel amplitude on the detection performance of linear modulation schemes. Finally, we present the statistical fading channel models for various fading scenarios and apply them to the performance analysis of digital wireless transmission, in terms of outage probability and average error rate.

Diversity combining is one of the most effective fading mitigation techniques. The basic design principle of diversity technique influences the development of several advanced wireless transmission technology. In this chapter, we study the design and analysis of fundamental diversity combining schemes. After discussing the basic implementation strategies, we investigate several conventional diversity combining schemes, including selection combining, maximum ratio combining, and thresholding combining. Special emphasis is put on the tradeoff analysis of performance versus complexity among different combining schemes. Finally, we presents the transmit diversity solutions for the multiple antennas at the transmitter scenario.

The wireless channel introduces frequency-selective fading to the transmitted signal when the channel coherence bandwidth Bc is smaller than transmitted signal bandwidth Bs. In this chapter, we discuss the challenges and candidate solutions for digital wireless transmission over frequency-selective fading channels. We first discuss the effects of selective fading on digital wireless transmission. We then present two classes of transmission technologies for frequency-selective fading channels, namely equalization and multicarrier transmission. Special emphasis was placed on orthogonal frequency division multiplexing (OFDM) technology, the practical discrete implementations of multicarrier transmission, as several advanced wireless systems adopt this transmission technology.

In this chapter, we present the principle of spread-spectrum transmission and demonstrate the basic underlying mechanisms for its desirable features. We first discuss the most popular spectrum spreading method, direct sequence spread spectrum (DSSS). Noting that the desirable features of spread spectrum system rely heavily on the spreading signal design, we then discuss the design of spreading codes. RAKE receiver and multiple user transmission based on DSSS are considered afterwards. We conclude the chapter with a brief discussion on frequency-hopping spread spectrum (FHSS).

Channel capacity characterizes the maximum transmission rate that a channel can support for error-free information delivery. As the performance upper limit for arbitrary transmission system, channel capacity provides valuable guidances for real-world transceiver design. The mathematical theory of channel capacity was established by Claude Shannon in the late 1940s, through his coding theorems. The advanced modulation and coding schemes developed afterward validate Shannon's pioneering vision. Error-control coding serves an effective capacity achieving solution. This chapter studies capacity and coding for wireless fading channels. We first discuss the capacity definition and sample error-control coding schemes for additive white Gaussian noise (AWGN) channels. We then present the commonly used capacity definition for both flat and selective fading channels. In addition to the ergodic capacity and capacity with outage, we also introduce and derive the optimal power and rate adaptation (OPRA) capacity. We conclude the chapter with the discussion of interleaving technique, which is widely used in wireless systems to mitigate the effect of deep fade on coded transmission.

Wireless channel introduces a time-varying gain to the transmitted signal. The dynamic range of channel power gain can be as much as 30 dB due to the fading effect. Adaptive transmission can achieve high spectral and power efficiency with guaranteed error rate performance over wireless fading channels. As such, adaptive transmission becomes an essential technology to meet the increasing demand for highly spectrum efficient wireless transmission. This chapter studies channel adaptive transmission techniques over frequency flat fading channels. We first present the basic idea of channel adaptive wireless transmission. We then separately discuss two classes of adaptive transmission technologies, namely rate adaptation and power adaptation. A joint discrete rate and continuous power adaptation design is also presented together with several implementation issues associated with channel adaptive transmission.

In this chapter, we study the fundamental principles of MIMO transmission and illustrate its performance advantages. We first introduce the flat fading MIMO channel model. Then, we present several MIMO transmission strategies exploring the diversity benefit inherent to MIMO channel. After that, we investigate the capacity potential of MIMO channel and study MIMO transmission strategies extracting the spatial multiplexing gains. The chapter is concluded with a characterization of the diversity-multiplexing trade-off.

Multiple-antenna transmission and reception techniques can improve both the reliability and efficiency of digital wireless systems. Due to the size, cost, and complexity constraints, it is in general challenging to implement multiple antennas at the mobile terminals. Meanwhile, considering the antennas at different mobile terminals together, we can create a multiple-antenna scenario, even if each terminal only has a single antenna. In this chapter, we introduce several advanced wireless transmission technologies that explore in one way or another multiple antennas at different mobile terminals to achieve diversity gain as well as multiplexing gain. In particular, we will investigate multiuser diversity transmission, cooperative diversity transmission, and multiuser multiple-input-multiple-output (MIMO) transmission technologies. Our study of these advanced technologies will serve as the applications of the general digital wireless transmission over fading channel framework that we established in the previous chapters. Due to space limitation, these discussions will be by no means comprehensive. Interested readers can refer to related literature for further details.